Seasonal variation in movements and survival of invasive Pacific rats on sub-tropical Henderson Island: implications for eradication

• Main Authors: Oppel, S, McClelland, GTW, Lavers, JL, Churchyard, T, Donaldson, A, Duffield, N, Havery, S, Kelly, J, Proud, T, Russell, JC, Bond, AL
• Format: Conference Object
• Language: English
• Published: IUCN 2019
• Subjects: Environmental Sciences; Environmental Science and Management; Conservation and Biodiversity; Pacific; Henderson Island
• Online Access: https://portals.iucn.org/library/node/48358; https://doi.org/10.2305/IUCN.CH.2019.SSC-OP.62.en; http://ecite.utas.edu.au/131231

Invasive rodents are successful colonists of many ecosystems around the world, and can have very flexibleforaging behaviours that lead to differences in spatial ranges and seasonal demography among individuals and islands.Understanding such spatial and temporal information is critical to plan rodent eradication operations, and a detailedexamination of an islands rat population can expand our knowledge about possible variation in behaviour and demographyof invasive rats in general. Here we investigated the movements and survival of Pacific rats ( Rattus exulans ) over fivemonths on sub-tropical Henderson Island in the South Pacific Ocean four years after a failed eradication operation. Weestimated movement distances, home range sizes and monthly survival using a spatially-explicit Cormack-Jolly-Sebermodel and examined how movement and survival varied over time. We captured and marked 810 rats and found a medianmaximum distance between capture locations of 39 25 m (0107 m) in a coastal coconut grove and 61 127 m (01,023m) on the inland coral plateau. Estimated home range radii of Pacific rats on the coral plateau varied between territorial(median: 134 m; 95% credible interval 106165 m) and roaming rats (median: 778 m; 2901,633 m). The proportion ofrats belonging to the roaming movement type varied from 1% in early June to 23% in October. There was no evidence tosuggest that rats on Henderson in 2015 had home ranges that would limit their ability to encounter bait, making it unlikelythat limited movement contributed to the eradication failure if the pattern we found in 2015 is consistent across years.We found a temporal pattern in monthly survival probability, with monthly survival probabilities of 0.352 (0.0810.737)in late July and 0.950 (0.8460.987) in late August. If seasonal variation in survival probability is indicative of resourcelimitations and consistent across years, an eradication operation in late July would likely have the greatest probability ofsuccess.